While much has been published or patented on the subject of PMA based catalysts and their uses as oxidation catalysts, to our knowledge there have been no fixed-bed plants in operation for methacrolein oxidation and no patents exist that set forth any procedure for maintaining the activity of a PMA based oxidation catalyst during shut-downs. Standard fixed-bed shutdown and holding procedures have been shown to be detrimental to catalyst performance. If the bath were to be cooled during a shutdown, to about 250.degree. C., catalyst maintenance might be possible, however, it would be both awkward and impractical to cool and/or drain the salt during each shutdown and, such a practice would likely require hours to accomplish.
Thus, the prior art of which we are aware has not set forth a method by which the activity of a PMA based catalyst can be maintained during reactor shutdown. To be useful, we believe the maintenance of PMA based catalysts during shutdown must be relatively inexpensive, simple and quick to accomplish without necessitating cooling or draining of the salt from the reactor bath.